Refinement of the Superstructure of C-Type Chromium(III) Tris(metaphosphate), Cr(PO₃)₃

Single crystals of Cr(PO₃)₃ suitable for X-ray investigations were obtained under various experimental conditions that favour volatilization of the phosphate and its recrystallization from the gas phase. The compound belongs to the series of phosphates M(PO₃)₃ (M³⁺ = Al, In, Sc, Ti, V, Fe, Mo, Rh, Ru) which adopt the C-type structure, characterized by one-dimensional infinite metaphosphate chains and isolated MO₆ octahedra. Associated with the superstructure generally found for this structure type, in which the monoclinic b axis is tripled, three crystallographically different CrO₆ octahedra of almost ideal geometry [d_ave(Cr-O) = 1.96 (2) Å] were observed. Within the two independent metaphosphate chains distinctly different bond distances from P to bridging and terminal O atoms were found. [d_ave(P-OXX tha ing of , phosphorus oxygen , respectively -O_b) = 1.58 (1) , d_ave(P-O_t) = 1.49 (1) Å].

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